652 Dynamic Theory. 



brain. The first effect of the electrical stimulation is hyperaemia, or an 

 increase of the blood supply to the part affected, which is seen in the 

 swelling of the arteries and the deepening of the color. Second, it is 

 shown that brain work has been done because there is a profuse flow of 

 venous blood from the sinuses (large veins ), which had been exposed in 

 the process of uncovering the brain, but which had ceased to bleed be- 

 fore the application of the galvanic shock. When through continued 

 hemorrhage the supply of blood was too much reduced to show signs of 

 continued pulsations, the current however strong failed to stimulate. 



When the two electrodes were placed on the cerebrum at some dis- 

 tance apart, the stimulation resulted in convulsions, and the further 

 apart they were the more severe the convulsions. These fits were always 

 preceded by a hyperaemic condition of the cortex of the cerebrum, "and 

 not only was there in every case a distinct interval between the applica- 

 tion of the electrodes and the first convulsive movement, but there was 

 occasionally a distinct interval of time after the withdrawal of the stim- 

 ulation, before the condition of the gray matter had reached the pitch of 

 tension requisite for an explosive discharge. This of itself is sufficient 

 to show that the effects were not due to conducted currents or direct 

 stimulation of the motor nerves of the muscles, but to an abnormal ex- 

 citability or irritability of parts whose function it might be inferred was 

 to initiate those changes which would result in the normal contraction 

 of the muscles affected." ( Carpenter.) 



In other words the galvanic stimulus acted upon the cortical motor 

 cells in such a way as to take the place of the ordinary stimulus from the 

 internal senses, or cerebral memory organs. For, as the experiments 

 prove, a part of the cortex is made up of organs for receiving, and 

 others for elaborating or co-ordinating external sensations ; and these 

 constitute the organs of the internal senses. Other cortical tracts appear 

 to be the starting stations for motor stimuli which pass thence down to 

 the medulla oblongata and on out to the muscles. The stimuli which 

 start here are made up in the internal sense organs, although their ele- 

 ments are derived originally from the environment through external 

 senses. When these same tracts are irritated by an interpolated stimu- 

 lation at all like that which they are accustomed to, they will react in 

 the usual way and produce the same motor acts. It has been shown 

 that the galvanic stimulation applied directly to muscles and to motor 

 nerves produced normal action, and the inference from all the experi- 

 ments seems to be warranted that the normal stimulation conveyed by 

 the sensory nerves is exceedingly like a galvanic interrupted current. 

 Carpenter observes that the ordinary circulation of the blood is sufficient 

 ' ' to keep up the tension of the ganglionic centers to the point required 

 for motorial discharge by automatic or volitional closure of the circuit," 



